In recent years, with the spread of mobile devices, such as cellular phones, or with an increase in the speed or the enhancement in the frequency of semiconductor devices, which are main components of personal computers, multilayer ceramic capacitors to be mounted on such electronic devices have been increasingly desired to reduce the size and increase the capacity, and dielectric layers constituting the multilayer ceramic capacitors have been desired to reduce the layer thickness and increase the number of layers.
Hitherto, dielectric materials containing barium titanate as the main ingredients have been used as dielectric ceramics serving as dielectric layers constituting multilayer ceramic capacitors. However, in recent years, dielectric ceramics containing crystal grains having a so-called core shell structure has been developed in which oxide powder of magnesium or rare earth elements are added to barium titanate powder to form a solid solution of the magnesium or the rare earth elements near the surface of the crystal grains containing barium titanate as the main ingredients and has been put into practical use as a multilayer ceramic capacitor.
Here, the core shell structure of crystal grains refers to a structure in which a core portion which is a the center of the crystal grains and a shell portion which is the outer shell portion of the crystal grains form phases that are physically and chemically different from each other. In the crystal grains containing barium titanate as the main ingredients, the core portion is occupied by a tetragonal crystal phase and, in contrast, the shell portion is occupied by a cubic crystal phase.
The multilayer ceramic capacitor containing, as dielectric layers, the dielectric ceramics constituted by the crystal grains having such a core shell structure has characteristics such that, with an increase in the relative dielectric constant, X7R (the temperature change ratio of relative dielectric constant based on 25° C. is within ±15% at −55 to 125° C.) is satisfied as temperature characteristics of relative dielectric constant and the change in the relative dielectric constant when increasing an AC voltage to be applied is small. However, when the dielectric layer thickness is reduced to about 2 μm, for example, there has been a problem in that the life characteristics in a high temperature load test sharply decrease.
[Patent-Document 1] Japanese Unexamined Patent Application Publication No. 2001-220224